Anchor bolts are used to secure a variety of structures including bridges; buildings; and towers including those for communications and wind turbine generators. Loose anchor bolts can lead to grout failure under the flange of the base section of the structure. Grout failure can ultimately lead to a structure that is not level, thus rendering the structure unsafe or inoperable
Loose anchor bolts are a compounding problem in that a loose anchor bolt tends to lead to the loosening of neighboring bolts. As more bolts loosen the problem is propagated and if left unchecked can lead to a catastrophic structural failure.
If loose anchor bolts are found, it can be from a multitude of reasons. Examples include but are not limited to failure of the supporting grout, failure of the supporting foundation such as fracturing or uneven settling, improperly tensioned anchor bolts from prior workmanship, long term anchor bolt relaxation and/or defective anchor bolts. It is important to establish precise records of the bolts tension to better determine if there are issues and the possible root of changes in bolt tension.
With regard to a wind turbine, synonymously referred to herein as a wind turbine generator or a WTG, a base section that is out of level by fractions of an inch will lead to several inches or feet out of level at the top of the tower. The generator, gearbox, bearings, and other components that rest at the top of the tower, must be precisely balanced for the wind turbine generator to operate properly. If such components are out of balance, it leads to the failure to one or more of the mentioned components and it is costly to fix such issues. Loose anchor bolts can ultimately lead to the collapse of the turbine, but are more often associated with failing concrete and/or grout under at the base of the tower. If bolts are left untensioned for a period of time, the bolts can weaken and eventually fracture, potentially leading to tower collapse.
Being able to determine and document the actual load that anchor bolts are holding is crucial to making educated decisions and assumptions about the anchoring system for the life of the structure and beyond. Prior art attempts to do so have involved implanted sensors and complex processes that are difficult to maintain and the inclusion of sensors within bolts actually reduces their effectiveness to bear the structure load.
Thus, there exists a need for a simple method to measure and monitor the tension on an installed anchor bolt of a structure. There also exists a need to improve structure lifetime through implementing a program of routine anchor bolt monitoring and retensioning.